


Three's a Party

by idontevenknowugh



Series: Numbers [2]
Category: Undertale (Video Game)
Genre: Dirty Talk, HoneyKustard, Humiliation, Implied/Referenced Cheating, M/M, Oral Sex, Rough Oral Sex, Threesome - M/M/M, Underfell Sans, Underswap Papyrus
Language: English
Status: Completed
Published: 2017-10-01
Updated: 2017-10-01
Packaged: 2019-01-07 18:59:33
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,533
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12238791
Author URL: https://archiveofourown.org/users/idontevenknowugh/pseuds/idontevenknowugh
Summary: Stretch has to confront his lovers, but it doesn’t quite end up like anyone expected.





	Three's a Party

**Author's Note:**

> A follow up to Two Timing, commissioned by sapphire-sphinx. Thank you so much for requesting these two fics. They were fun!

“Well, consider my lesson learned,” Stretch opened with a wry smile. He leaned down to kiss Sans, then Red, both of whom were waiting on his couch. It had been a full day since his evening with Edge and Papyrus, but he was still kind of sore. He refused to give it away to his lovers by reacting to the pain bending caused. 

“Lesson?” Red asked, breaking the kiss as soon as it started. Stretch could see Sans nodding along out of the corner of his sockets. 

“Heh,” Stretch gave them a ‘are you kidding me?’ look. “No need to be coy. I'm very aware how lucky I am to have you two in my life. It had me scared for a bit, though, all that talk of cheating. Never would have guessed your brothers could act, or do-” 

“Woah.” Sans put up a hand to stop him. “Our brothers? What about them?”

“Yeah, what the fuck are you on about, Stretch?” Red added, his relaxed posture disappearing.

“About Edge and Papyrus…” Stretch said slowly, “because I called you guys lazy…” He looked between the two shorter monsters with a growing sense of horror. 

“You didn't get them to fuck me?” He asked, voice quiet from the panic that was setting in. 

Two sets of blank sockets met his question. Stretch hunched down into himself with the agonizing realization that he had just admitted to cheating on his lovers with his lovers’ brothers. To his lovers. 

He was going to be sick. 

“I'm going to kill my brother,” Red snarled with an impressive amount of heat. Edge and Red were often swapping insults and threats, but the same brotherly affection they all had usually ran below it. This time he just sounded furious. Stretch’s anxiety grew. 

“No,” Sans put up a calming hand towards Red. Stretch relaxed a little. Of course Sans would be take a more reasonable approach- “I'm going to kill your brother.” 

“Hey!” Red jumped to his feet. “Your brother did it too!” 

“Only because Edge tricked him into it, and you know it!” Sans retorted. Stretch opened his mouth to refute that, but hesitated to get into the middle of this particular fight. What he really needed was a way to defuse it.

“Oh as if anyone could get your thick-skulled idiot of a brother to do anything he didn't already want to.” Red rolled his eyelights. 

“Don't you dare,” Sans’s hands clenched into fists. 

“Guys!” Stretch yelled, soul tight. This was quickly getting into relationship- possibly monster- ending territory. “I- it was just a misunderstanding.”

“How exactly did they fuck you by mistake?” Red asked flatly, his ire redirected towards Stretch. 

That was a very good question, and one that Stretch blushed to answer. His reaction to being gaged and striped hadn't exactly been… good. Then again… 

“Well, first, they accused me of cheating,” Stretch pointed out. 

“That’s rich,” Sans said, hands on his crests. Stretch grimaced. He would be happy to appreciate the irony later, if he got through this with the best thing that had ever happened to him intact. 

“Not on both of you, I mean, not together.” Stretch rubbed his skull. “You don't want to tell them we’re all together. If one of them figured out I was dating the other…”

Red and Sans grew visibly uncomfortable as Stretch talked. It had been a small point of contention when they all decided to do this. Red and Sans’s friendship had been well established. So, anxious about explaining multiple partners to their brothers, they had omitted that piece, only telling them about Stretch. Even that had taken some convincing. Papyrus and Edge had been sworn to keep things quiet and shouldn't have been able to learn about the other one, but they had. It was the only explanation. 

“Oh,” Sans deflated. He looked anxiously over at Red. Red was glaring very hard at his own shoes. Stretch’s soul ached, but they hadn't sorted things out to the point he could go to them. 

“Guess we should go… fix that…” Red muttered. He sounded miserable. Stretch didn't want to heap on any blame, so he waiting in awkward silence for one of them to speak.

“Why didn't you say anything to them?” Sans asked finally. 

He should have expected that. He had expected to need to explain his role, but he still hesitated. 

“I was… gagged,” he started slowly. Red and Sans looked at each other and then back at him.

“Oh fuck, did they…?” Sans looked like he was going to be sick. Red was shaking his skull, a far away look in his sockets. 

“No, look. They were- how they treated me was- I thought you guys had to have planned it.” Stretch blushed. “So I went for it…” 

There was a fresh round of silence in response to that. 

“So, what you’ll just spread them for anyone?” Red snarled. Stretch flushed with embarrassment and anger. 

“Of course not! It's only because I thought you-” he cut himself off with a huff. He had thought wrong. That was on him. 

“Stretch,” Sans opened his arms and stepped forward. “I see the misunderstand…ings that caused this, but it is a little worrying that you would-” 

“Actually,” Red interrupted Sans with a hand on his shoulder. “It’s kind of hot.” 

Sans was looking at him like he was crazy, which Stretch could understand. Where the hell had that come from?

“You find him having sex with our brothers hot?” Sans asked tersely. 

“No! No. No.” Red lifted his hands and waved them. “Not that.” He grinned that wicked grin that always sent shivers down Stretch’s spine. “It's hot that he’d do it if we told him to.”

Sans looked back at Stretch, who now had to be blushing furiously. That wasn't exactly what Stretch was trying to achieve by explaining things. 

“I think we just need to accept that our boyfriend is a slut,” Red sauntered over to Stretch as he talked. He reached up and pulled a startled Stretch into a kiss. 

Stretch was having trouble understanding why Red’s tongue was halfway down his throat. They were mad at him. Red had just called him a slut! Not that Stretch’s magic was interested in proving that little piece of wisdom wrong. He whimpered into the kiss as arousal started to seep into his bones, making him feel weak. 

“And he’s” Red broke the kiss and licked his mandible, “our slut.” 

Stretch looked at Sans out of the corner of his sockets. Except he wasn't there. Had he left? Was that the last straw? Panicked, Stretch pulled away from Red and looked around. It didn't take long to find him. He had snuck around behind Stretch. 

“If that’s the case,” Sans grumbled, his face bright blue, “then I would feel better if we reminded him of that fact.”

“Heh, now we’re talking,” Red smirked, and Stretch found himself falling backwards. 

Sans caught him with a grunt, arms wrapping around his ribs. Sans lowered them down slowly until Stretch was laying, propped up against him. 

Red, meanwhile, dropped to his knees between Stretch’s legs. His expression was hungry, all sharp teeth and wide, intense eyelights. Anyone with any sense would be terrified to see it. Stretch fucking moaned under his breath, his legs twitching wider to accommodate him. 

“I-I’m sorry,” Papyrus whined, turning to look at Sans. “I'm so sorry.”

“I know.” He kissed the side of Stretch’s skull. “But we’re going to take you,” Sans whispered against him, “so thoroughly you won't even remember what it feels like to be with anyone else.”

“Oh fuck,” Stretch could feel his breath speeding up with his soul, but he wasn't sure if it was from fear or excitement. Red leaned forward, placing a hand to either side of Stretch, boxing him in. Stretch felt cornered, trapped between his lovers.

When Red pressed their mouths together, it wasn't the chaste kiss they had shared before this all started. It wasn't even the demanding one he’d used before. This kiss was a savage claiming of Stretch’s mouth that made him melt into Sans. His entire focus narrowed to that point of contact with Red. 

So, it came as a bit of a surprise to him when his pants were pulled down, Red breaking the kiss to move enough to slide them off. Stretch shivered, cold air and hot memories hitting his pelvis simultaneously. 

Red returned to his spot, bringing Stretch back to the present by roughly grabbing his legs and spreading them just to the edge of pain. Stretch gasped, wriggling his pelvis in an attempt to get away, but Sans was behind him, holding him in place. Deep orange magic suffused his cheekbones at being so exposed. 

His magic, practically sparking with excitement, hovered around his pelvis. Red gave it that hungry grin and ran a finger up the part bulging out of his pelvic inlet. It jumped to oblige, forming into moist folds. Red snorted and used all the phalanges of one hand to spread them open momentarily before the slick magic escaped, falling closed again. 

Red tisked and sat back on his heels. 

“Well that’s not very accommodating,” he mused, looking up past Stretch to Sans. “I think the slut should help me get a good look at our pussy.” 

“Oh my god,” Sans muttered, embarrassment in his voice. Still, he shifted against Stretch, rubbing a very telling bulge against his spine. 

“You want me to… what?” Stretch asked, not quite sure he had heard right. 

“What are you?” Red asked, instead of answering him.

“Red,” Stretch whined. 

“Stretch,” Red mocked, leaning forward and pressing his hand against Stretch’s clit, hard. Stretch wailed, his pelvis jerking as he simultaneously tried to move towards that delicious pressure and away from the overwhelming sensation. 

“Woah,” Sans’s arms tightened around Stretch’s ribs, keeping him still. As Stretch jerked, he kept rubbing against Sans’s cock, drawing moans from behind him. 

“What are you?” Red asked again, smirking wickedly, as he drew his hand away, strings of liquid clinging to it before breaking. Stretch’s pelvis dropped like a stone. He was panting, dizzy, and unbelievably aroused. 

“I- it’s too embarrassing,” Stretch complained.

“I guess no more for you, then,” Red smirked, and looked past him again to Sans. “Wanna go fuck?”

“Fuck yeah,” Sans almost moaned, right against Stretch’s skull. Some deep part of him knew that they were just teasing him, that this was his punishment, rather than any of the more devastating options. That part wasn't very articulate at the moment, and the thought of being left here alone was almost painful.

“I’m sorry, I’m sorry,” he begged, looking at each of his lovers. “Please, I’m- I’ma slut… your slut.”

Red’s eyelights dropped down to him, and he smirked. 

“You are, aren't you?” He asked, as if it hadn't been his idea all along. He reached out and flicked Stretch’s clit. Stretch yelled, twisting uselessly as the sting faded. 

“Now, why don't you spread those lips,” he added once Stretch had calmed down. Stretch flushed, but he reached down, hooking his arms under his legs. He couldn’t quite reach like that, so he hiked up his legs, holding them with his arms. Trembling, he felt along his pelvis until he met the softness of his magic.

With some wetness lining his sockets, he pulled the magic apart, baring his pussy to Red. There was a long whistle, quite a feat for a skeleton.

“Holy shit, Stretch. That might actually be the hottest thing I’ve seen… ever.” 

Stretch felt, impossibly, more heat in his face, which was shamefully mirrored in his pelvis. He felt like his magic was gushing under the gaze. Red was probably watching arousal ooze out of him. 

“I want to see,” Sans huffed, practically humping Stretch’s back as he tried to peer over his shoulder.

“You’ll have to put on a show for Sans sometime,” Red told Stretch, freeing his cock. “Now that you know your place.”

He crawled forward so he was sitting right in front of Stretch. It was maddening to have to guess what was Red’s member grazing his magic and what was wishful thinking. Stretch thrust his pelvis up towards him, begging for attention. 

“Looking for something?” Red asked, drawing his hips away slightly. 

“No,” Stretch panted, trying to wiggle out of Sans’s grasp, who grabbed fistfuls of Stretch’s sweatshirt.

“Ah, ah,” Sans pulled their bodies back together with a thump. “Be a good…slut.” He sounded just as embarrassed by the term, but with a husky quality that did nothing to help Stretch’s state. 

Which was still on display.

Stretch relaxed his arms and legs, just barely, but Red noticed instantly. He grabbed each leg and pushed back, pressing them into his ribs. Stretch gasped, his fingers twitching reflexively against his own pussy. 

“Gotta keep them open if you’re going to get what you want.” 

“B-but you… you…” Stretch panted, unable to put his thoughts into any kind of order for speech. He found it very unfair that Red was holding that over him when he wasn't ready to deliver. 

“Go on, ask for it- or better yet, beg for it,” Red prompted him. Stretch sagged against Sans with a humiliated groan. That explained his restraint, when Red was usually the first one with his dick out. 

This was right in Red’s comfort zone, unlike Stretch and Sans. They had done some light role play, blindfolds and shit. Stretch had liked it a lot and told them as much, leading to the confusion before. It had never been mean like this, however, never meant to humiliate anyone.

Stretch had a brief flash of stubbornness, so he didn't beg for it. He turned and pressed his teeth to Sans instead. His other lover was more than happy to oblige him with a kiss. Stretch deepened it, drawing Sans into a sloppy, awkward make out session that prevented him from giving into Red for several long moments. Red, never one to take the back seat, broke through the sound of their tongues lapping and teeth clacking.

“Oh damn.”

Stretch glanced over at Red. If he had been frustrated by Stretch’s dodge, he wasn’t showing it now. He was staring at them with eager sockets, one hand stroking his cock lazily. He and Edge really were related, weren't they? 

Shame, cold and shocking crashed through him, washing away his embarrassment. He shouldn't even know that. Breaking the kiss with Sans, Stretch took a breath to steady himself. He loved Red and Sans, and he would do anything for them, no matter how degrading. 

“P-please…” his voice still shook. Gritting his teeth, he readjusted his hands until his pussy was as spread as it could be. He blushed and glanced to the side, unable to keep eye contact with Red while he said it.

“Please fuck me.” Sans gasped, but Stretch thought that he could do better. For them. “I want your cock- cocks… in me,” he stumbled. “Please… destroy me-”

“You should see your pussy,” Red sounded smug to a degree Stretch had never heard before. “Though I suppose I shouldn't be surprised that our slut loves begging for cock.” 

He moved back towards Stretch, at least, though he leaned past him to kiss Sans. It was enough for his magic to press against Stretch’s. Groaning, he trust up into the contact, hoping for more, much more. What was really embarrassing was that Red was right. Stretch was desperately horny. The more he submitted to his lovers, the more they debased him, the deeper his arousal got. 

“Ah! Please put it in me,” he begged, with much less hesitation, and thrust up as hard as he could. Red’s moan was muffled by Sans’s mouth. He broke the kiss to look down at Stretch. Instead of making more snarky comments, he kissed Stretch, and there was movement by his pelvis. 

Red’s cock was just thick enough to fill him without hurting. Stretch tried to force his mind away from comparisons, but it wasn't easy to ignore how much more careful Red was, even after all of that. He slid into Stretch slowly, as unnecessary as it probably was. Stretch was fucking soaking wet. 

“Sans, lay him down,” Red instructed, once he had pressed all the way in. Sans made a noise of agreement, and Stretch tipped backwards, guided to the ground by Sans’s hands. Stretch stared up at the ceiling, still holding his legs up and open, though he’d lost hold of his pussy. It was a lot less interesting than looking at Red, who was still not moving at all. 

“Red-” Stretch didn't get to complain because another cock, this one a deep blue, was on his face. Not in his mouth, just resting on him. The juncture where it met Sans’s pelvis was right in front of his sockets, the length running down over his nose and across his mouth. 

“Don't forget about Sans,” Red teased. “You love his cock too, don't you?” 

“Yes,” Stretch breathed, extending his tongue to lick at it, even wrapping it as far around the rock hard member as he could. Sans groaned, pelvis shifting as if he could fuck Stretch’s tongue. Which was just silly, so Stretch opened his mouth, tongue stretched out to rest along the underside of Sans’s cock. 

“Shit,” Sans didn't waste any time drawing back just enough to clear Stretch’s jaw and tongue and thrust into his mouth. Stretch drew his tongue back in and went to work, lathering attention on the member while it slid out and back in. 

Red, however, wasn't moving at all. Stretch waited as long as he could, which felt like hours and was likely seconds, before he started to wiggle his pelvis in an attempt to thrust against him. 

“Something wrong, Stretch?” Red asked casually, as though he wasn't putting his own pleasure on hold to tease him. Stretch couldn't do anything but whine around Sans’s cock and wiggle more. Sans moaned, leaning forward to thrust deeper. 

“I did what you wanted, right?” Red was starting to fall to the background behind the wet sounds of Sans fucking his mouth. 

Stretch let go of his legs, intending to wrap them around Red and make himself clear, but Red caught one, then the other, and pushed them back up, leaning on them as he finally started to move. 

They were true to their promise, at least. He couldn't remember his own name, let alone anything else while they fucked him. Red was setting a punishing pace that made some soreness blossom across his pelvis. Sans was filling Stretch’s mouth and brushing the back of his skull mercilessly. 

And Stretch loved it. 

He writhed, caught between the competing need to get Red a little deeper, a little harder into him and the need to get Sans off and fill his mouth with his lover’s musky cum. Not that he really had any choice in these matters. Red and Sans had taken over completely. 

“Watching…… him……. hot,” Red said something above him, and then the sounds of them using him was joined by the wet sound of kissing, punctuated by little moans and hums of pleasure.

Then Sans got a whole lot louder. He broke off from Red and leaned down to grip Stretch’s skull. His pelvis sped up, moving jerkily. 

“Stretch, it’s- I’m-” 

Stretch moaned around Sans’s cock. He used his tongue to urge Sans along, and soon the hot, salty cum was flooding his mouth. He drank it up greedily, almost choking on it. In response to Sans finishing, Red sped up, absolutely pounding into Stretch. It drove Stretch to his orgasm, and he hurried to swallow the last of Sans’a release before a wail of pleasure ripped out of him. 

“Fuck!” Red came to a stuttering stop, and Stretch felt his cum fill him up down there as well. 

Stretch’s body tensed, arching up with his orgasm before it relaxed, leaving him feeling positively boneless. Red’s magic softened in him and slipped out. Stretch could feel their mingled juices trickling down his pelvis without it there to hold them in. It felt shamefully good, even though it tickled. Stretch shivered. His legs stretched back out, stiff and aching, but he didn't care. He felt satisfied. He felt used. 

He felt content. 

“I don't think he’a going anywhere anytime soon,” He tuned in to hear Sans talking to Red. 

“Good point,” Red flopped down, letting gravity position him to Stretch’s right. “And I think he’s got the right idea.”

“Stretch, are you okay?” Sans asked, getting down on the floor to his left, though he didn't lay back. Stretch felt a pang of guilt that Sans was worrying about him. Reaching up, he pulled Sans to laying and kissed him. 

“Better than okay,” he murmured when the kiss broke. “As long as we- as you guys aren't…” he couldn't say it.

“We ain't mad,” Red said sleepily. He hugged Stretch from behind, nuzzling into his back. “Wuzza misunder… we’ll be open…” And he was out. 

Stretch shared a smile with Sans, who nodded at him. 

“Yep, exactly that.”

**Author's Note:**

> My tumblr is where I: take requests, post streams, chit chat, do teasers, try out new fics, reblog a lot of skeleton porn, pimp all my favorite fics


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